1. Field of the Invention
The present invention relates to a method, apparatus and computer program for image resolution conversion, and especially for converting an input image having a first resolution to an output image having a second different resolution.
2. Description of Related Art
Many kinds of matrix display devices having fixed resolutions are known, for example, a liquid crystal display (LCD) device having a resolution of "640 dots (horizontal).times.480 lines (vertical)", a plasma display device having a resolution of "800 dots (horizontal).times.600 lines (vertical)", etc. For displaying various kinds of input images having various resolutions on these matrix display devices having various resolutions, a method of performing twice-writing of pixels for scaling up the input images has been used and also a method of performing thinning out pixels for scaling down the input images has been used.
Japanese Kokai 7-104,710 (published on Apr. 21, 1995) and No. 8-137,444 (published on May 31, 1996) disclose multi-scanning display methods and apparatuses for a liquid crystal display using a technique, for example, when data of 5 pixels thin out to data of 4 pixels, the width of each pixel is magnified by 5/4, then the resulting data are averaged and outputted as output data of each pixel. These conventional methods and apparatuses have recently appeared which make it possible to cope with plural input images having different resolutions by providing plural circuits each of which converts a particular input resolution, and by selectively using one of these circuits.
Thus, the conventional resolution converting methods and apparatuses provide one dedicated resolution converting circuit for each input resolution, and switch over among the plural resolution converting circuits according to the resolution of an input image. Therefore, such methods have a disadvantage that these circuits must become large to cope with many input resolutions.
Moreover, each of the conventional resolution converting methods and apparatuses has a disadvantage in that a great number of resolution converting circuits must be individually prepared for magnifying a part of the matrix display device. In practice, it is difficult to smoothly scale up and down the input images.